Hydroxyethyl (meth)acrylate is a colorless and clear liquid with double functional groups in the molecules, and has a two-stage curing reaction function. It is one of the most valuable special (methyl)acrylates that has been studied mostly around the world. It is mainly used for the preparation of hydroxyl acrylic resins. The polymers of hydroxyethyl (meth)acrylate have special gloss, transparency and weather resistance. In the pharmaceutical industry, the autopolymers of hydroxyethyl methacrylate can be used for dental materials and orthopedics materials as they have no physiological rejections. With the development of the downstream industries, the application of the monomer is still increasing.
There are many methods for preparation of hydroxyethyl (meth)acrylate, and the common one used in the industrial production at present is the method of ring-opening reaction: in the reactor, EO is added dropwise to the (meth)acrylic acid as per a certain ratio of ethylene oxide (EO) and (meth)acrylic acid, and reacted to synthesize hydroxyethyl (meth)acrylate under the combined effect of a catalyst and a polymerization inhibitor.
CN101891613A discloses a method for preparing hydroxyethyl methacrylate: a flask equipped with a stirrer, a thermometer and a reflux condensing tube was placed on a water bath, ferric oxide, hydroquinone and methacrylic acid were added, the mixtures were heated to 80-85° C. by the water bath, the air in the flask was replaced by nitrogen, ethylene oxide was inlet after the ferric oxide was completely dissolved in the methacrylic acid, the time for inletting the ethylene oxide was 4 hours, the reaction was continued for 1 hour after the completion of the inletting of ethylene oxide, the reactants were then placed in a distillation flask, an appropriate amount of hydroquinone was added for reduced pressure distillation, and the fraction of 82-85° C. was collected as the product.
CN102584579A also discloses a preparation process of hydroxyethyl methacrylate characterized in that the reactor is vacuated by vacuum units and is kept in vacuum to make methacrylic acid, a catalyst, a polymerization inhibitor and water sucked to the reactor, then the vacuum degree of the reactor is kept between −0.99 Mpa and 0.75 Mpa, and then it is heated to 80-85° C., ethylene oxide is added dropwise, the pressure inside the reactor is ensured to be less than or equal to 60 KPa by controlling the dripping speed of the ethylene oxide, the dripping speed of the ethylene oxide need to be adjusted with continuing of the reaction and change of the reaction rate, and the reaction temperature is controlled at 90-100° C. by cooling with cooling water; after the completion of adding the ethylene oxide dropwise, the cooling water is shut off and the temperature is naturally raised, and sampling and detecting whether the mass percentage of methacrylic acid is less than 0.5 percent after the temperature is lowered, and if so, an addition reaction is deemed to be ended; and after the addition reaction is completed, the light component ethylene oxide, water and methacrylic acid are removed under reduced pressure, the intermediate product is transferred into a middle kettle, 0.5-5 wt % water is added, and then it is distilled under reduced pressure to obtain hydroxyethyl methacrylate.
The processes reported at present are mainly processes of batch tank type reactors. There are slight differences in the selection of process parameters such as a catalyst, a polymerization inhibitor, reaction temperature and reaction time. However, the reaction efficiency of the batch tank type reactors are low, and continuous production cannot be processed.
If the processes of stirring tank type reactors are used, the disadvantages are low reaction efficiency, a large amount of gas phase ethylene oxide and by-products such as diesters, monoesters, and static electricity is easy to be generated while the stirring rotating for a long time to easily cause the gas phase EO to explode, thus it is very dangerous; as the reaction progress, the reaction rate is changed, and the adding rate of EO needs to be adjusted at all times, so the operation is complex; and the cost of the investment of the devices are high. The problems of a very low reactant concentration and a very low reaction rate also exist for the continuous reactors, thus continuous production cannot be processed.
Although continuous production can be achieved by using tubular reactors, if stirring tank type reactors are simply replaced by the tubular reactors, when (meth)acrylic acid and EO are fed, the concentration of the EO is high, explosion will happens easily; the synthesis of hydroxyethyl (meth)acrylate is a strong exothermic reaction, and when the concentration of EO is high, the reaction rate will be too fast, thus too much heat will be released, there will be a risk of temperature runaway; and a too high concentration of EO will result in a further reaction between the generated hydroxyethyl (methyl)acrylate and EO to produce diglycol (meth)acrylate, causing the yield of the product to decrease; furthermore, under the condition of constant temperature, the conversion rate of (meth)acrylic acid and EO at the end of the reaction is low, a lot of (meth)acrylic acid is left, and it will be more difficult for the subsequent separation.
Therefore, a new process for preparing hydroxyethyl (meth)acrylate is needed to overcome the above disadvantages in the prior art.